The present invention relates to a viewing optical system for viewing an object image formed on a focusing screen, and an imaging apparatus comprising the same.
So far, a single-lens reflex camera used as an imaging apparatus making use of a film or electronic imaging device has comprised an image erection optical system such as a penta roof prism and an eyepiece lens system adapted to guide a light beam leaving that image erection optical system to the eyeball of a viewer for the purpose of viewing an object image on a focusing screen onto which a subject image is projected via a taking lens.
Such viewing optical systems include those designed to make the refractive index of a prism material so high that an optical path for the image erection function of the prism is easily achievable, as set forth in the following patent publications.
[Patent Publication 1]
JP(A)59-148021
[Patent Publication 2]
JP(A)61-156017
[Patent Publication 3]
JP(A)2005-284039
[Patent Publication 4]
JP(A)2005-55874
However, the eyepiece lens system of the viewing optical system set forth in each patent publication has a longer focal length, and when it is intended to obtain a viewing image having a wide field of view, there is no option but to increase image size on a focusing screen: it is unsuitable for diminishing prism size. On the other hand, digital single-lens reflex cameras are now in wide use as imaging apparatus. However, imaging plane size is smaller than that of a conventional Leica size film: when the aforesaid viewing optical system is used, the viewing angle of field tends to become small.
The present invention has for its object the provision of a viewing optical system that, albeit being of small size, enables subjects to be easily viewed over a wide view of field by some significant tweaks to a lens system while taking advantage of the merit of making sure an optical path length by use of a prism having a high refractive index, and an imaging apparatus comprising the same.